1. Field of the Invention
The invention relates to small and smallest microphones (micro-microphones), which are worn on the clothing or often directly on the body, for example, in the hair, of the user.
2. Description of the Related Art
Such micro-microphones comprise commonly one, less commonly, two or more membranes which are usually placed over cutouts in the mantle of the cylindrical microphone. This configuration provides an inner hollow space between the end plate, the bottom plate, and the housing mantle with the openings covered by the membranes. This inner hollow space is required and essential for the acoustic properties of the microphone.
It is important in connection with this inner hollow space that it has a pressure that is as close as possible to the barometric pressure of the ambient in order to maintain the membranes, when at rest, in a predetermined and precisely defined position as well as in a defined tension state.
In order to achieve this goal, it has been common practice to provide small openings usually within the area of the membrane attachment but also directly within the membranes. These small openings then allow pressure compensation.
However, due to the special applications of these microphones, it happens frequently that moisture enters the inner hollow space through these openings and condenses there, thus causing problems for the membrane and the other microphone components. One has to take into consideration that these microphones, for example, during song performances or theater or musical performances, are worn by the singers and actors directly on their skin or in the hair. These types of microphones are thus subjected to much greater adverse effects than conventional microphones. This is also evidenced in that the average service life of such microphones in the theater is usually not even a month so that there exists a strong economical interest to solve the aforementioned problems.
It must be taken into consideration that the length as well as the diameter of the completely assembled microphone is only a few millimeters.
It is an object of the present invention to increase the average service life of microphones of the aforementioned kind while maintaining their small size and their acoustic properties.
In accordance with the present invention, this is achieved in that the inner hollow space is connected by a component of high acoustic impedance with a compensation chamber that is moisture-tightly sealed by a flaccid diaphragm relative to the ambient.
With this measure it is achieved that a complete closure of the microphone interior relative to the exterior (ambient) is realized. Furthermore, by providing a component with high acoustic impedance, which functions in the present case similarly to a low-pass filter, the acoustic properties of the inner hollow space and thus of the entire microphone will not change because, for the frequencies to be transmitted during operation, the component will act similarly to a closed wall as a result of its high impedance.
Moreover, the compensation chamber and the flaccid diaphragm ensure that the ambient pressure will deform the diaphragm to such an extent that the barometric ambient pressure is always present in the interior of the microphone.
As a component of high acoustic impedance it is preferred to employ a pressure compensation tube having an inner diameter in the range of approximately 70 xcexcm and a length of 3 to 4 mm. However, it is also possible to provide a stopper or the like made of open-pore foamed material or the like. It should be noted though that the tube is the preferred embodiment with respect to acoustic properties.
The flaccid closure diaphragm must essentially only fulfill the requirements of being impermeable to moisture and of being as flaccid as possible, i.e., being formed without tension and being mounted without tension. It is provided only to separate and protect the compensation chamber from the ambient.
It is possible to employ conventional materials as they are used in the field of electro-acoustics for the novel components employed according to the invention. The flaccid diaphragm, for example, can be made of polycarbonate, polyurethane, rubber or elastomer, but also of metal foils. The tube can be made of corrosion-resistant materials such as German silver, stainless steel, or plastic.